Process and product of tanning with condensation products of polyhydric phenols with methylol dicyandiamide or methylol dicyandiamidine compounds



United States Patent Ernst Honold and Arthur Miekeley, Frankfurt am Main, Fechenheim, Germany, assignors to Cassella Farbwerke Mainkur Aktiengesellschaft, Frankfurt am Main, Fechenheim, Germany, a company of Germany No Drawing. Application January 12, 1954 Serial N0. 403,662

Claims priority, application Germany January 19, 1953 6 Claims. (Cl. 8-94.24)

The present invention relates to condensation products soluble in water and useful as tanning agents for hides and skins and a process for manufacturing these condensation products.

We have found that valuable tanning agents are obtained by condensing the methylol compounds (e. g. monoor dimethylol compounds) of dicyandiamide or dicyandiamidine or their mixtures, with polyhydric phenols.

In order to obtain products being water-soluble in the acidic pH-rauge, it is sufficient to introduce an aqueous solution of the methylol compound into a polyhydric phenol (e. g. resorcinol, pyrocatechol) and to standardize the solution by means of a weak or strong acid or acidic salt to show an acidic reaction. The condensation occurs already at room temperature, e. g., 20 (3., and is preferably effected below 50 C. in order to avoid the formation of insoluble products. Preferably each methylol group is condensed with /2 to 1 mol of polyhydric phenol. The solutions thus obtained may be directly used for tanning purposes. But they may also be concentrated by evaporation in vacuum, advantageously at a temperature below 50 C., so that the new tanning agents are obtained in a solid state.

The new tanning agents are of an unlimited solubility in water when in the acidic pH-range and possess a very good storage life. They exert a strong coagulating action on albumin so that they can be used for tanning (also without an addition of bicarbonate or common salt) in an equal manner as tanning agents of a vegetable origin. They furnish leathers which are well filled, of a light color and of a cation-active character and therefore these leathers can be dyed and greased like chrome-tanned leather.

The leathers produced according to the invention are distinguished by a high alkali resistance. For this reason the new tanning agents are particularly suitable for the manufacture of leather to be used for inner soles.

Because anionic tanning agents, such as tanning agents of a vegetable origin or in particular the sulfitized vegetable tanning extracts as well as synthetic tanning agents containing sulfonic acid groups, or also sulfite cellulose extracts are precipitated by the cation-active tanning agents obtained according to the present procedure, the two types of tanning agents cannot be used at the same time in one bath for tanning. However when causing them one after the other to act upon the skin, either by tanning it at first with anionic tanning agents and by after-tanning it with the tanning agents produced according to the present process or proceeding in the reverse order, a mutual fixation of the tanning agents takes place in the leather, whereby especially well-filled leathers with low losses during washing are obtained.

The following examples and description of tanning are given to illustrate the invention but are not intended to limit it thereto, the parts and percent are by weight and all temperatures in degrees centigrade.

EXAMPLE 1 84 parts of dicyandiamide are dissolved with parts of 40% formaldehyde and parts of Water by heating the mass shortly. The solution having cooled again to room temperature, 55 parts of resorcinol are added, followed by acidifying with about 5 parts of glacial acetic acid. The solution thus obtained is almost colorless and capable of dilution with water at any ratio. It represents an excellent tanning agent.

I Instead of the acetic acid used, the condensation may also be carried out by adding 5 parts of ammonium chloride at about 40.

If in this example parts of resorcinol (instead of 55 parts) are used, a solution of quite similar valuable tanning properties is obtained.

Instead of resorcinol there may be similarly successfully applied e. g. phloroglucinol, pyrocatechol and its alkyl homologues'.

EXAMPLE 2 84 parts of dicyandiamide are heated with 100 parts of ion hydrochloric acid and 100 parts of water on a water bath until an exothermic reaction occurs. On cooling, alkali is added for neutralizing, 80 parts of 40% formaldehyde are added, and by heating the mass to 70 an aqueous solution of the methylol compound is produced. On cooling, 110 parts of resorcinol are introduced and thereafter 5 parts of glacial acetic acid added. The solution obtained possesses valuable tanning properties.

Also in this example the resorcinol may be replaced by other polyhydric phenols. Furthermore, the condensation may also, be effected by the addition of an acidic salt or a mineral acid.

' 100 parts of water and 2030 parts of a condensation product obtained according to the above examples, in such a Way that the solution of the tanning agent is added slowly in several portions during some hours to the tanning liquor. After 24 hours of milling, the operation of tanning is completed for skins being not too thick. After 1-2 days of storage and paring, the leather is Well rinsed, eventually neutralized with l2% of ammonium carbonate and then dyed, greased and finished by usual methods. A well-filled, soft leather of a good handle and tearing strength is obtained.

We claim:

1. In the process of tanning a skin, the steps which comprise adding, at a temperature range between 20 and 50 C., 0.5-1 mole of a polyhydroxy benzene selected from the group consisting of dihydroxy benzene and trihydroxy benzene to an aqueous solution of 1 mole of a compound selected from the group consisting of monomethylol dicyandiamide and monomethylol dicyandiamidine, condensing at said temperature range the compound and the polyhydroxy benzene in an acid medium and tanning a skin with the resultant solution.

2. In the process of tanning a skin the steps which comprise adding, at a temperature range between 20 and 50 0., 05-1 mole of resorcinol to an aqueous solution of 1 mole of a compound selected from the group consisting of monomethylol dicyandiamide and monomethylol dicyandiamidine, condensing at said temperature the compound and the resorcinol in an acid medium and tanning a skin with the resultant solution.

3. In the process of tanning a skin the steps which comprise adding, at a temperature range between 20 and of 1 mole of a compound selected from the group eonsisting of monomethylol dicyandiarnide and monomethylol dicyandiamidine, condensing at said temperature the compound and the pyrocatechol in an acid medium and tanning a skin with the resultant solution.

4. The product obtained from the process of claim 1. 5. The product obtained from the process of claim 2. 6. The product obtained from the process of claim 3.

References Cited in the file of this patent UNITED STATES PATENTS 1,912,593 Pollak June 6, 1933 Hershberger Aug. 20, 1940 DAlelio Mar. 30, 1943 Gundel Jan. 4, 1944 Bock et a1. Feb. 29, 1944 Scott Sept. 16, 1947 Roesti Feb. 22, 1949 Anthony et a1. Mar. 7, 19-50 FOREIGN PATENTS Great Britain 2'. June 28, 1944 Germany Nov. 14, 1930 

1. IN THE PROCESS OF TANNING A SKIN, THE STEPS WHICH COMPRISE ADDING, AT A TEMPERATURE RANGE BETWEEN 20 AND 50*C., 0.5-1 MOLE OF A POLYHYDROXY BENZENE SELECTED FROM THE GROUP CONSISTING OF DIHYDROXY BENZENE AND TRIHYDROXY BENZENE TO AN AQUEOUS SOLUTION OF 1 MOLE OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF MONOMETHYLOL DICYANDIAMIDE AND MONOMETHYLOL DICYANDIAMIDINE, CONDENSING AT SAID TEMPERATURE RANGE THE COMPOUND AND THE POLYHYDROXY BENZENE IN AN ACID MEDIUM AND TANNING A SKIN WITH THE RESULTANT SOLUTION. 